Method of applying a retention ring to a disc rotor assembly

ABSTRACT

A retention ring ( 1 ) is applied to a disc rotor assembly ( 3 ) which comprises a plurality of substantially equiangularly spaced magnets ( 7 ). The ring is expanded by driving it over a tapered mandrel ( 13 ) onto a rim ( 5 ) of the rotor assembly.

The present invention relates to a rotor for a rotary electrical machinesuch as an electrical generator or electric motor.

British Patent Specification GB 2 222 031 A describes an axial fieldelectrical generator capable of operation at very high speeds. Thisdocument describes an axial field electrical generator having a discrotor with a ring of permanent magnet segments equiangularly spacedaround a hub. Engagement with the hub is maintained by means of apre-stressed hoop. The hoop is formed initially as a push fit andstressed during assembly by expanding the hub by forcing into it, anoversize boss.

As a practical matter, this means of retention has severe disadvantageswhich have been overcome by the present invention.

Thus, a first aspect of the present invention provides a method ofapplying a retention ring to a disc rotor assembly comprising aplurality of substantially equiangularly spaced magnets, the methodcomprising expanding the retention ring by driving it over a taperedmandrel and onto a rim of the rotor assembly.

The complete rotor assembly may be used in any kind of electricalmachine which utilizes a disc-type rotor, for example as described in GB2 222 031 A or in the applicants' co-pending UK patent application No.9123576.2 (GB 2 261 327 A). In such machines, usually a plurality of therotors are spaced apart along a drive shaft, interspersed by thinannular stators.

Prior to fitment of the retention ring, it is preferred for the magnetto be maintained in position on a hub of the rotor by a temporaryretention means, for example a temporary holding ring located over therim of the rotor. It is also preferred to provide a second (outer)containment ring slidably located over the temporary holding ring,outside the tapered mandrel by means of push fit. When the retentionring is driven over the mandrel, the retention ring can then displacethe outer containment ring so that the retention ring grips thetemporary holding ring, and hence the rim of the rotor, through themandrel by means of interference fit.

It is also convenient to support the retention ring on a slidablesupport means, for example a slidable support ring between itself andthe tapered mandrel. The slidable support ring can then be driven overthe rotor together with the retention ring so that it is trapped betweenthe mandrel, the inner ring and the rotor itself.

After assembly, the temporary retention ring and slidable support ringcan be machined smooth so that they do not obstruct the rotor in use.

The slidable support ring is preferably rested on a driver means such asa hollow driver cup partially surrounding the mandrel. Normally, thering and driver means is acted upon by one part of a ram, for examplemechanical or hydraulic, and a second part of the ram acts on themandrel.

The present invention will now be explained in more detail by thefollowing non-limiting description of a preferred embodiment and withreference to the accompanying drawings, in which:

FIG. 1 shows a tapered mandrel arrangement for effecting a method offitting a retention ring in accordance with the present invention;

FIG. 2 shows the arrangement of FIG. 1 with the retention ring over therotor prior to removal from the mandrel.

As shown in the drawings, a retention ring 1, preferably wound fromcarbon fibres, is to be fitted over a disc rotor 3 having a rim 5. Therotor comprises a plurality of substantially equi-angularly spacedmagnets fitted on a spider 9.

Referring now to FIG. 1, prior to assembly the rotor is located withinan upper (wider) part 11 of a tapered mandrel 13. The upper part of themandrel is in contact with one half 15 of a mechanical or hydraulic ramoperated press. A lower (narrower) part 17 of the mandrel faces a secondhalf 19 of the ram, spaced apart therefrom.

The retention ring 1 is supported concentrically on the mandrel 13 bymeans of a slidable concentric metal support ring 21 over which it islocated by means of a push fit. Initially, the retention ring andsupport ring are a loose fit over the mandrel, approximately two thirdsdown the length thereof. The magnets of the rotor are held on the spider9 by means of a temporary holding inner metal ring 23 also concentricwith the mandrel. A containment ring 25 outside the mandrel surroundsthe inner ring 23 and the rim 5 of the rotor. The containment ring 25prevents the inner ring 23 from buckling as the retention ring andsupport ring are driven over it, as described below.

The support ring 21 is supported by a hollow driver cup 27 surroundingthe lower part 17 of the mandrel. The base 29 of the driver cup is indirect contact with the second half 19 of the ram.

As shown in FIG. 2, actuation of the ram to bring the two halves 15, 19of the ram closer together causes the support ring 21 and with it theretention ring 1, to travel over the mandrel 14 towards the wider part11 until the containment ring is upwardly displaced. The containmentring is dimensioned to slide freely over the wider part 11 in order notto impede positioning of the retainment ring 1 over the rim 5. Theretention ring 1 and support ring 21 then grip the inner ring and rim 5of the rotor through the mandrel.

The assembled rotor is then cut free of the mandrel and support ring 21and inner ring 23 are machined down prior to assembly of the rotor intoan electrical machine so that the rotor does not have protrusions whichwould interfere with the stator(s) thereof.

In the light of this disclosure, modifications of the describedembodiment, as well as other embodiments, all within the scope of thepresent invention as defined by the appended claims, will now becomeapparent to persons skilled in the art.

What is claimed is:
 1. A method of applying a retention ring to a discrotor assembly comprising a plurality of substantially equiangularlyspaced magnets, the method comprising supporting the retention ring on aslidable support, the slidable support located between the retentionring and a tapered mandrel; and expanding the retention ring by drivingthe slidable support and the retention ring over the tapered mandrel andonto a rim of the rotor assembly.
 2. A method according to claim 1,wherein the magnets are maintained in position on a hub of the rotorprior to fitment of the retention ring by temporary retention means. 3.A method according to claim 2, wherein the temporary retention meanscomprises a temporary holding ring located over the rim of the rotor andan outer containment ring slidably located over the temporary holdingring.
 4. A method according to claim 3, wherein the retention ringdisplaces the outer containment ring so that the retention ring gripsthe temporary holding ring by interference fit.
 5. A method according toclaim 1, wherein the retention ring is driven over the tapered mandrelby a ramming mechanism.
 6. A method according to claim 5, wherein theretention ring is connected to the ramming mechanism driver means.
 7. Amethod according to claim 5 or claim 6, wherein the ramming mechanism isa mechanical or hydraulic ram.
 8. A method according to claim 6 whereinthe driver means is arranged to act on the slidable support and theslidable support is a slidable support ring.
 9. A method according toclaim 8 wherein the slidable support ring is driven over the rotor to betrapped between the rotor rim and the retention ring.
 10. A methodaccording to claim 1 wherein the slidable support is a slidable supportring.
 11. A method according to claim 2 wherein the slidable support isa slidable support ring.
 12. A method according to claim 3 wherein theslidable support is a slidable support ring.
 13. A method according toclaim 4 wherein the slidable support is a slidable support ring.
 14. Amethod according to claim 12 wherein after assembly the rotor is removedfrom the mandrel and the temporary holding ring and slidable supportring are machined smooth.
 15. A method according to claim 13 whereinafter assembly the rotor is removed from the mandrel and the temporaryholding ring and slidable support ring are machined smooth.
 16. A methodaccording to claim 10 wherein the slidable support ring is driven overthe rotor to be trapped between the rotor rim and the retention ring.